UC  SOUTHERN  REGIONAL  LIBRARY  FACIUTY 


AA    001  185  733    i 


Issued  January  27, 1911. 

U.  S.  DEPARTMENT  OF   AGRICULTURE, 

OFFICE  OF  PUBLIC  ROADS— Circular  No.  93. 
LOGAN  WALLER  PAGE,  Director. 


BITUMENS  AND  THEIR  ESSENTIAL  CONSTITU- 
ENTS FOR  ROAD  CONSTRUCTION 
AND  MAINTENANCE. 


BY 


PRfiVOST  HUBBARD, 


CHEMIST,     OFFICE     OF    PUBLIC     ROADS. 


WASHINGTON: 

GOVERNMENT    PRINTING   OFFICE. 
1911. 


SRLF     0^ 


LETTER  OF  TRANSMITTAL 


U.  S.  Department  or  Agriculture, 

Office  of  Public  Roads, 

Washington^  D.  C.^  December  5,  1910. 
Sir:  I  have  the  honor  to  transmit  herewith  the  manuscript  of  a 
circular  by  Mr.  Prevost  Hubbard,  chemist  in  this  office,  entitled 
"  Bitumens  and  Their  Essential  Constituents  for  Road  Construction 
and  Maintenance."  This  publication  presents  in  condensed  form  a 
description  and  discussion  of  various  bituminous  materials  at  present 
in  use  in  road  construction  and  maintenance.  It  should  be  of  great 
service  in  clearing  up  a  very  general  misunderstanding  concerning 
the  actual  and  comparative  value  of  bituminous  road  materials,  and 
also  the  meaning  of  certain  terms.  I  respectfully  request  that  it  be 
issued  as  Circular  93  of  this  office.  In  view  of  the  newness  of  the 
subject  and  lack  of  complete  data,  some  of  the  statements  made  may 
in  the  future  require  modification.  This  circular  will  therefore  be 
revised  from  time  to  time  in  order  to  keep  it  abreast  with  the  latest 
information  obtainable. 

Respectfully,  Logan  Waller  Page, 

Director. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 

eHOSO"— Cir.  93— 11  3 


BITUMENS  AND  THEIR  ESSENTIAL  CONSTITUENTS  FOR  ROAD 
CONSTRUCTION  AND  MAINTENANCE. 


So  much  confusion  exists  among  road  engineers  and  others  in- 
terested in  bituminous  road  binders  concerning  the  meaning  of  cer- 
tain terms  as  applied  to  these  materials  that"  it  has  seemed  advisable 
to  present  in  brief  form  the  definitions  of  such  terms  as  at  present 
used  by  the  United  States  Office  of  Public  Roads.  It  should  be  un- 
derstood, however,  that  these  definitions  are  at  present  more  or  less 
arbitrary,  owing  to  wide  differences  of  opinion  held  by  those  who  are 
considered  authorities  on  the  subject  of  bitumens.  Notwithstanding 
these  facts,  it  is  hoped  that  this  circular  will  furnish  highway  en- 
gineers and  other  interested  persons  with  a  foundation  for  acquiring 
and  systematically  classifying  further  information  along  the  lines 
herein  indicated.  To  aid  them  in  this  matter  a  brief  discussion  of 
the  value  of  the  various  materials  used  in  road  construction  has  been 
given  in  addition  to  the  definitions. 

Acid  Sludge. — A  mixture  of  sulphonated  hydrocarbons  resulting 
from  the  treatment  of  bitumens  with  sulphuric  acid;  usually  a  waste 
or  by-product  obtained  in  this  manner  from  the  purification  of  tar 
and  oil  distillates.  Wlien  sufficiently  concentrated  these  sulphonated 
products  become  viscous  and  gunniiy.  They  are  readily  attacked 
by  water  and  are  therefore  unsuitable  for  use  as  enduring  road 
binders. 

Anthracene. — A  waxy  crystalline  hydrocarbon  having  the  chemical 
formula  C14H10,  found  in  tars,  principally  coal  tars  which  have  been 
produced  at  high  temperatures.  Anthracene  is  believed  to  be  of  no 
practical  value  in  road  binders. 

Artificial  Asphalt. — See  As))lialts  and  Oil  Asphalts. 

Artificial  Bitumens. — Hydrocarbon  distillates  and  residues  produced 
by  the  partial  or  fractional  distillation  of  bitumens,  and  hydrocarbon 
distillates  produced  by  the  destructive  distillation  of  bitumens,  i)yro- 
bitumens,  and  other  organic  materials,  such  as  wood,  bone,  etc.  Na- 
tive bitumens  which  have  been  treated  merely  for  the  removal  of 
water  and  extianeous  organic  and  inorganic  materials  should  not  l>e 
classed  as  artificial  products,  but  as  refined  native  bitumens. 

Asphalts. — Solid  or  semisolid  native  bitumens,  consisting  of  a  mix- 
ture of  hydrcK-arbons  of  complex  structnre,  largely  cyclic  and  bridge 
compounds,  together  with  a  small  proportion  of  their  sulphur  and 
nitrogen  derivatives,  but  free  from  any  appreciable  amount  of  solid 

[Cir.  0.'!]  5 


6  niir.MiNs  rou  i{t».\i)  coNsi  itrci  ION. 

parartins,  moltini;'  upon  tlu'  applirat imi  of  lu'iii  and  cvulcutly  pi'o- 
duoetl  by  nature  from  i^etroliMnus  coiitainiu":  little  or  no  solid  paraf- 
fins. Solitl  or  stMui>oli(l  ivsidut's  pi-oduci'd  from  i)i()l»al)ly  similar 
t>ils  by  artifu-ial  prorossos  are  sometimes  called  as|)lialts.  hut  should 
more  properlv  1h'  termed  oil  as|)halts.  'I'he  more  rouimou  types  of 
native  asphalts  are  known  hy  the  name  of  tiie  locality  in  which  they 
tH'our,  such  as  Trinidad,  lUMinudez.  Maracaiho.  Cuban.  California,  etc. 
Native  asphalts  with  few  e.xceptions  contain  water,  extraneous  or- 
ijanic  or  ve<i:etable  matter,  and  inor<ranic  matter,  such  as  clay,  sand, 
etc.  A  large  projiortion  of  these  impurities  is  removed  l)y  a  rough 
refining  process  without  otherwise  changing  the  character  of  the 
a>phalt. 

Native  asj)halts  are  usually  too  hard  to  be  used  as  road  ijinders 
without  tirst  fluxing  them  with  a  lieavy  petroleum  residuum  and  thus 
j)roducing  an  asphaltic  cement.  Artificial  asphalts  are,  as  a  rule, 
brought  to  suitable  consistenc}'^  during  the  process  of  manufacture. 

Asphaltenes. — A  term  commonly  aj)plied  to  those  hydrocarbons  in 
petroleums,  petroleum  products,  malthas,  asphaltic  cements,  and  solid 
native  bitumens  which  are  soluble  in  carbon  bisulphide  but  insoluble 
in  paraffin  naphtha.  As  a  rule  paraffin  naphthas  of  different  specific 
gravities  and  boiling  points  dissolve  different  amounts  of  hydrocar- 
bons in  a  given  bitumen,  and  the  heavier  the  naj)htha  and  the  higher 
its  boiling  point  the  greater  is  its  solvent  action.  It  is  evident,  there- 
fore, that  the  percentage  of  asphaltenes  will  vary  with  the  gravity 
and  boiling  point  of  the  naphtha,  and  for  this  reason  it  would  seem 
well  to  substitute  for  the  term  asphaltenes,  ''  bitumen  insoluble  in 
paraffin  naphtha,"  with  a  statement  of  the  gravity  of  the  naphtha 
used  and  the  temperatures  between  which  it  boils.  The  presence  of 
najihtha  insoluble  hydrocarbons  is  supposed  to  give  body  to  the 
product  in  which  they  occur  and  to  be  accountable  to  a  great  extent 
for  its  binding  value.  They  show  no  binding  value,  since  many  of 
them  are  hard  and  brittle,  but  they  produce  adhesive  mixtures  when 
fluxed  with  certain  heavy  oils.  As  a  rule,  for  a  given  type  of  bitu- 
men hardness  increases  with  the  percentage  of  bitumen  insoluble  in 
a  given  naphtha.  The  so-called  asphaltenes  are  not  found  to  any 
extent  in  native  bitumens  with  a  paraffin  base,  but  occur  principally 
in  asphalts,  malthas,  asphaltic  petroleums,  and  in  blown  petroleum 
residues.  They  vary  chemically  and  physically  with  the  product  in 
which  the}'  occur,  and,  therefore,  do  not  represent  definite  chemical 
compounds. 

Asphaltic  Petroleums. — Asphaltic  petroleums,  or  asphaltic  oils,  are 
petroleums  containing  an  asphaltic  base — i.  e.,  they  are  capable  of  pro- 
ducing residues  very  similar  to  native  asphalts  if  evaporated  or  dis- 
tilled down  to  the  consistency  of  such  asphalts.     They  contain  little 

'  See  Bitumens. 
[Cir.  93] 


BITUMENS   FOR   BOAD    CONSTRUCTION.  7 

or  no  solid  paraffins  and  are  thus  differentiated  from  paraffin  petro- 
leums. Native  asphalts  are  probably  produced  from  such  oils  by 
natural  processes. 

Asphaltic  Cement. — The  term  asphaltic  cement  was  originally  applied 
to  a  product  obtained  by  fluxing  an  asphalt  with  a  sufficient  quantity 
of  heavy  residual  oil  or  flux  to  produce  a  binder  of  suitable  con- 
sistency for  paving  purposes.  In  its  broadest  sense  it  may  be  applied 
to  all  semisolid  bitumens  of  an  asphaltic  nature  which  are  of  suitable 
consistency  for  use  as  binders  in  street  or  road  construction,  whether 
prepared  by  fluxing  a  solid  native  or  artificial  bitumen  or  by  reduc- 
ing an  asphaltic  or  semiasphaltic  petroleum  bj^  distillation  or  other 
process. 

Baume  Gravity. — An  arbitrary  scale  of  specific  gravity  or  density  of 
liquids,  usually  expressed  as  degrees  Baume  or  °  B.  This  scale  is 
commonly  used  in  connection  with  oil  products.  For  liquids  lighter 
than  water  the  scale  begins  at  10°  B.,  which  represents  the  specific 
gravity  of  water,  or  1.0000.  As  the  Baume  degrees  increase  the 
specific  gravity  decreases.  The  following  formulae  are  used  in  con- 
verting Baume  degrees  for  liquids  lighter  than  water  into  direct 
specific  gravity  and  vice  versa : 

Sp.  S'i''  =  i3o+oB  ^^  1'^-^''  ^• 

°B  =  ^^^^    -130  at  17.5°  C. 
fep.  gr. 

For  liquids  heavier  than  water  the  scale  begins  at  0°  B.,  which  rep- 
resents the  specific  gravity  of  water,  or  1.0000.  In  this  scale  the 
degrees  Baume  increase  with  the  specific  gravity.  The  following 
formulae  are  used  in  converting  Baume  degrees  for  liquids  heavier 
than  water  into  direct  specific  gravity  and  vice  versa : 

145 

oB  =  U5-J^^  at  1.5.5°  C. 
bp.  gr. 

Benzol. — A  volatile  colorless  fluid  hydrocarbon  of  characteristic 
odor  having  the  chemical  formula  CoHq.  It  occurs  mainly  in  crude 
coal  tars  and  water-gas  tars,  and  boils  at  80.4°  C,  so  that  it  is  re- 
moved in  the  first  fraction  when  these  tars  are  subjected  to  the 
process  of  distillation.  Benzol  is  an  active  solvent  fot  most  bitumens. 
It  is  sometimes  called  benzene,  but  should  not  be  confused  with 
benzine,  which  is  the  term  applied  to  the  lighter  and  more  volatile 
fractions  of  petroleum. 

[Cir.  93] 


8  BITUMKNS    Von    KOAD    lONS  IIUCTION, 

Bitumen,  -liituiiu'iis  arc  mixtiirt's  of  iiativo  ov  pyro<jiMu*tic  hyilro- 
oarlwus  and  their  ilorivativos,  which  may  Im'  "fuses,  liquids,  viscous 
liniiiils,  or  soliils.  If  solids,  they  melt  more  or  less  readily  upon  the 
application  of  heat  and  are  soluble  in  earhon  hisiilphide,  ehloroform, 
and  similar  solvents.  They  may  he  divided  into  two  main  classes — 
(1)  native  hitumetis  and  CJ)  artificial  hitiimcns.  Bitumens,  b('in«j; 
mixtures  of  hydrocarbons,  can  have  no  melting  i)oint,  although  this 
term  is  often  iised  to  denote  the  tem|)erature  at  wMiich  they  soften 
sufficiently  to  flow. 

Bituminous.  A  term  api)lic(l  not  oul>'  to  materials  or  objects  wliich 
contain  bittmien.  such  as  bituminous  rock,  bituminous  macadam,  etc., 
but  also  to  certain  pyro-bitumens,  such  as  bituminous  coal,  which  give 
rise  to  the  formation  of  l)itumens  upon  being  sui)jected  to  the  process 
of  destructive  distillation. 

Blown  petroleum. — T^lown  petroleums,  which  are  often  called  blowm 
oils,  are  ]ieir«)leum  rcsiduums  through  which  a  jet  of  air  has  been 
passed  during  or  just  after  distillation.  The  blowing  process  causes 
certain  chemical  reactions  of  a  complicated  nature  to  take  place  and 
results  in  thickening  or  increasing  the  consistency  of  the  oil  to  an  ex- 
tent depending  upon  its  temperature  and  the  amount  of  blowing  which 
it  receives.  Semisolid  and  solid  products  are  thus  often  formed  from 
fluid  residuums.  If  the  oil  is  asphaltic  or  .semiasphaltic  in  nature, 
asphaltic  cements  may  be  produced  in  this  manner.  Blown  oils  are 
characteristically  short  or  nonductile  when  semisolid,  although  they 
may  possess  considerable  binding  value  if  not  originally  of  a  paraffin 
nature.  Blowing  an  oil  usually  increases  its  percentage  of  hydrocar- 
bons insoluble  in  any  given  paraffin  naphtha. 

Carbenes. — A  term  conuuonly  applied  to  those  hydrocarbons  in  pe- 
troleum, petroleum  products,  malthas,  asphaltic  cements,  and  solid 
native  bitumens  which  are  soluble  in  carbon  bisulphide  but  insoluble 
in  carbon  tetrachloride.  The  presence  of  an  appreciable  amount  of 
these  hydrocarbons  indicates  that  the  material  in  which  they  occur 
has  been  subjected  to  unnecessarily  high  temperatures.  Cracked  oil 
residuums  -^how  an  increase  in  carbenes  in  proportion  to  the  extent 
of  cracking  and  the  formation  of  these  products  is  evidently  a  near 
step  to  coking.  But  little  is  known  of  their  effect  upon  the  value  of 
a  bitumen  for  road  construction,  but  they  are  generallv  looked  upon 
with  suspicion  and,  in  certain  specifications  for  asphaltic  cements, 
their  prc<enco  has  been  limited  to  a  low  percentage. 

Carbon  Bisulphide. — This  substance,  sometimes  called  carbon  disul- 
phide,  is  a  volatile  and  extremely  inflammable  compound  of  carbon 
and  sulphur,  boiling  at  47°  C.  and  having  the  chemical  formula 
CS....  Pure  carbon  bisulphide  is  a  colorless  mobile  liquid  having  an 
ethereal  odor.     It  is  one  of  the  most  active  solvents  for  bitumens 

[Cir.  9.3] 


BITUMENS    FOR    ROAD    CONSTRUCTION.  9 

and  is  commonly  employed  for  this  purpose  in  the  detennination  of 
total  bitumen. 

Carbon  Tetrachloride. — A  volatile  noninflammable  compound  of  car- 
bon and  chlorine,  boiling  at  76°  C.  It  is  a  colorless  mobile  liquid 
with  an  odor  similar  to  that  of  chloroform,  to  which  it  is  closely 
related,  and  has  the  chemical  formula  CCI4.  It  is  an  excellent  sol- 
vent for  bitumens,  but  is  not  usually  as  powerful  as  carbon  bisul- 
phide. It  is  employed  in  bitumen  analysis  for  the  determination  of 
carbenes  or  hydrocarbons  soluble  in  carbon  bisulphide  but  insoluble 
in  carbon  tetrachloride. 

Coal  Tar. — A  mixture  of  hydrocarbon  distillates,  mostly  unsaturated 
ring  compounds,  produced  in  the  destructive  distillation  of  coal. 
Crude  coal  tar  is  a  black,  more  or  less  viscid  fluid  having  a  gassy 
odor  and  varying  in  specific  gravity  from  1.10  to  1.25  and  sometimes 
higher.  It  always  contains  a  certain  amount  of  ammoniacal  water 
which  makes  it  unsuitable  for  use  as  a  road  binder.  When  reduced  to 
proper  consistency  by  distillation,  coal  tar  makes  an  excellent  bitumi- 
nous road  binder,  providing  it  does  not  carry  too  high  percentages 
of  free  carbon  and  naphthalene.  The  composition  of  coal  tar  varies 
according  to  the  coal  from  which  it  is  produced  and  the  method  of 
distillation.  Tars  produced  at  high  temperatures  contain  a  large 
amount  of  free  carbon  and  usually  run  high  in  naphthalene,  while 
those  produced  at  low  temperatures  carry  less  free  carbon  and  as 
a  rule  less  naphthalene.  Low  temperature  coal  tars  are  therefore 
most  suitable  for  the  preparation  of  road  binders.^ 

Coke-Oven  Tar. — Coal  tar  produced  from  by-product  coke  ovens  in 
the  manufacture  of  coke  from  bituminous  coal.  This  process  of  coke 
manufacture  is  essentially  the  same  as  that  of  coal  gas.  Larger 
charges  of  coal  are,  however,  carbonized  in  the  former,  and  as  a  rule 
carbonization  is  conducted  at  a  lower  temperature  than  in  the  manu- 
facture of  coal  gas.  The  resulting  tar  therefore  contains  a  smaller 
amount  of  free  carbon,  averaging  from  3  to  10  per  cent,  and  is  better 
suited  for  the  preparation  of  road  binders  than  most  gas-house  coal 
tars. 

Cracked  Oil. — The  term  cracked  oil,  as  applied  to  road  binders,  refers 
to  petroleum  residuums  which  have  been  overheated  in  the  process 
of  manufacture.  Overheating  causes  a  breaking  down  of  certain 
constituents  of  the  oil,  which  results  first  in  the  formation  of  carbenes 
and  later  of  coke  or  free  carbon.  Badly  cracked  residuums  are  be- 
lieved to  be  inferior  road  binders. 

Cracking. — The  process  of  breaking  down  a  hydrocarbon  molecule 
by  the  application  of  heat.  This  may  result  either  in  the  formation 
of  other  hydrocarbon  molecules,  at  least  one  of  which  is  unsaturated 

>  See  Refined  tar. 
[Cir.  9:1] 


10  UnrMKNS    Ft»IJ    ItoAD    (ONsnU'c    IMON. 

niul  >ho\\>.  a  lii«:lu'r  raiio  of  r:irl)t)ii  to  livdro^t-ii  than  tlu*  ori<2;iniil 
uioKh-uK',  ov  t'lsi>  ill  tlu>  ili>ni|)lioii  of  tli.>  luolfciilc  iulo  its  cliMuonts, 
livdroiTon  aiul  c-arboii.  In  tho  latlor  case  tho  proi-rss  is  said  to  bo 
lU'stnu'tivo.  I'll*'  nioiT  Nolatilc  ami  cluMnicaliy  stable  hyib'ocarbons 
can  Ih»  orurkoti  onlv  at  tt'inpnat  uro  aboxc  tlicii-  lioilini,^  points.  In 
tlu>  ilistillation  of  oils  this  is  arfoniplishi'd  bv  c-ausin^^  condonsation 
to  take  plaiv  in  the  still  luul  nllo\vin«;  tlu*  condensed  oils  to  fall  back 
into  the  residue,  the  temperature  of  which  is  considerably  higher 
than  their  boilin*;  points.  In  i-arbureted  water-nfas  manufacture,  oils 
are  cracked  by  vaporizin<;  them  at  a  nnich  hi<j;her  temperature  than 
their  boilin<r  points.  The  heavier  oils  will,  however,  crack  at  tem- 
peratures below  their  normal  boilin<j  points,  and  this  is  particularly 
true  of  asphaltic  oils,  which  have  to  be  distilled  very  carefully,  some- 
times under  reduced  pressure,  in  order  to  produce  residuums  which 
are  not  cracked. 

Cut-Back  Products. — Petroleum  or  tar  re.siduums  which  are  cut  back, 
or  fluxed,  to  the  desired  consistency  with  a  distillate.  Volatile  dis- 
tillates are  employed  for  this  purpose  in  the  preparation  of  road 
binders,  when  it  is  desired  to  have  the  binder  increase  in  consistency 
or  become  harder  after  application.  In  such  cases  a  residuum  of 
proper  consistency  for  a  road  binder  is  cut  back  merely  for  the  pur- 
pose of  facilitating  application. 

Dead  Oils. — Heavy  oils  distilled  from  tars  at  between  170°  and 
270^  C.  with  a  density  greater  than  water.  These  oils,  if  free  from 
naphthalene,  serve  as  an  excellent  flux  in  the  preparation  of  cut-back 
road  binders  from  tar  pitches,  which  are  too  brittle  for  this  purpose. 

Destructive  Distillation. — A  process  of  distilling  organic  materials 
in  which  the  identity  of  the  material  distilled  is  destroyed,  resulting 
in  the  formation  of  tarry  distillates  and  a  coke  residue. 

Dehydrated  Tar. — Crude  tar  from  which  all  water  has  been  removed 
by  distillation  and  mechanical  contrivances  known  as  separators. 

Emulsions. — Oily  substances  made  miscible  with  water  through  the 
action  of  a  saponifying  agent  or  soap.  Petroleums  and  tars  may  be 
emulsified  by  this  means  and  such  emulsions,  if  properly  prepared 
from  good  materials,  are  often  serviceable  in  the  treatment  of  roads. 
The  majority  of  road  emulsions  can  be  considered  only  as  dust  pallia- 
tives and  temporary  binders. 

Fixed  Carbon. — The  residual  coke  obtained  upon  burning  hydro- 
carbon jjroducts  in  a  covered  vessel  in  the  absence  of  free  oxygen, 
according  to  an  arbitrary  method.  As  applied  to  bituminous  road 
materials,  the  determination  of  fixed  carbon  would  seem  to  be  of  value 
in  connection  with  petroleum  and  asphaltic  products  only.  Paraffin 
hydrocarbons  produce  little  or  no  fixed  carbon,  while  those  of  as- 
phaltic character  show  a  very  considerable  amount,  depending  upon 
the  percentage  of  asphaltic  compounds  present  and  the- consistency  of 

[Clr.  9.3] 


BITUMENS   FOR  ROAD   CONSTRUCTION.  11 

the  material.  The  fixed  carbon  determination  therefore  indicates 
the  mechanical  stability  and  body  of  such  materials.  It  is  not,  how- 
ever, an  extremely  accurate  determination  and  should  not  be  too 
strongly  relied  upon.  Since  fixed  carbon  is  a  product  formed  by 
ignition,  it  should  not  be  confused  with  free  carbon,  which  is  a 
material  already  existing  in  suspension.  The  presence  of  any  consid- 
erable quantity  of  free  carbon  vitiates  a  fixed  carbon  determination. 

Flux. — As  aj)plied  to  road  binders,  this  term  covers  fluid  oils  and 
tars  which  are  incorporated  with  asphalts  and  semisolid  or  solid  oil 
and  tar  residuums  for  the  purpose  of  reducing  their  consistency. 
Fluid  petroleum  residuums  are  commonly  employed  as  fluxes  in  the 
preparation  of  asphaltic  cements.  A  good  flux  produces  an  abso- 
lutely homogeneous  bituminous  mixture.  Both  petroleum  and  tar 
fluxes  will  produce  such  mixtures  with  native  and  artificial  as- 
phalts, but  most  fluid  petroleum  products  will  not  flux  tar  pitches 
satisfactorily. 

Free  Carbon. — Organic  matter  in  tars  which  is  insoluble  in  carbon 
bisulphide.  This  material  is  an  inert  black  powder,  which  is  held  in 
suspension  by  the  tar  proper,  and  probably  consists,  not  only  of  free 
carbon,  but  also  of  hydrocarbons  extremely  rich  in  carbon.  It  has 
no  binding  value  and  serves  no  useful  purpose  in  a  road  binder  other 
than  to  act  as  a  filler.  It  gives  the  tar  in  which  it  occurs  a  false 
consistency,  reduces  the  binding  capacity  of  the  tar,  and  probably 
interferes  with  its  penetration  into  and  absorption  by  the  road  stone 
or  road  surface.  The  maximum  allowable  limit  of  free  carbon  in 
road  binders  would  seem  to  be  about  20  per  cent. 

Gas-House  Coal  Tar.^ — Coal  tar  produced  as  a  by-product  in  the 
manufacture  of  illuminating  gas  from  coal.  The  modern  gas-house 
coal  tar  is  usually  produced  at  high  temperatures  and  therefore 
carries  a  percentage  of  free  carbon  varying  from  20  to  30  per  cent 
and  higher.  Unless  it  is  produced  at  low  or  medium  temperatures 
and  contains  less  than  20  per  cent  free  carbon,  it  is  not  well  suited  for 
the  preparation  of  a  dust  palliative  or  road  binder  by  direct  distil- 
lation. High-carbon  tars  may,  however,  be  combined  with  low- . 
carbon  tars  in  such  proportion  as  to  produce,  when  distilled  to  proper 
consistency,  excellent  road  binders  carrying  less  than  20  per  cent  free 
carbon. 

Gilsonite. — A  very  pure  solid  native  bitumen  possessing  many  of  the 
characteristics  of  asphalt.  It  differs  from  most  of  the  native  asphalts 
by  being  more  brittle,  having  a  higher  melting  or  softening  point, 
and  being  much  less  soluble  in  86°  B.  paraffin  naphtha.  When  fluxed 
with  certain  petroleum  residuums  it  j)r()duces  excellent  asphaltic 
cements.  In  the  preparation  of  road  binders  it  is  extensively  used 
for  the  purpose  of  reinforcing  blown  oils,  with  which  it  combines  to 


1  Sec  Coal  tar. 

[Cir.  93] 


12  BITUMENS   FOU    KOAD   fONSTRrCTlON. 

fi)rm  rublHM'v  stMiiisidiil  mixture-.  Such  |irr|):u:iti()ns  arc  Miiuotiim's 
termed  mineral  rubber. 

Grahamite.  A  pure  solid  iiativi«  bihuiitMi.  black  and  brittle,  which 
diH'>  iu)t  null  roailily,  but  iiitunicsccs  at  hiirh  temperatures.  It  is 
tlitferentinted  from  ixilsonitc  and  the  ii:i(i\i'  asphalts  by  the  fact 
that  it  is  almost  insoluble  in  paratlin  naphtha.  It  has  been  produced 
at  hi«rh  temperatures,  as  e\  idenced  by  the  percentage  of  cnrbenes 
which  it  contains,  and  some  varieties  closely  approach  the  pyro- 
bitumens  in  characteristics.  It  has  been  used  to  s<ime  extent  in  the 
preparation  of  asphaltic  cements,  but  up  to  the  present  has  been  little 
u.sed  in  the  manufacture  of  road  binders. 

High-Carbon  Tars. — Tars  containinir  a  hiirh  percentaije  of  free  car- 
I'on  -al)ove  I'O  per  cent.  Iligh-carbon  tars  are  produced  at  high 
temperatures  during  the  destructive  distillation  of  coal  and  are  of 
inferioi-  <|uality  for  use  as  dust  palliatives  and  road  binders. 

Hydrocarbons. — Chemical  compouiuls  comjiosed  of  the  elements 
hydrogen  and  carbon.  There  is  practically  an  unlimited  number  of 
such  compounds,  which  vary  greatly  in  physical  and  chemical  charac- 
teristics. Complex  mixtures  of  hydrocarbons  constitute  by  far  the 
greater  proportion  of  all  bitumens. 

Low-Carbon  Tars. — Tars  containing  a  low  percentage  of  free  car- 
bon— less  than  10  per  cent.  Low-carbon  tars  are  produced  at  com- 
paratively low  temperatures  during  the  destructive  distillation  of 
coal,  and  also  In'  cracking  oil  vapors  during  the  manufacture  of  car- 
bureted water  gas.  As  a  rule  they  are  more  suitable  than  high- 
carbon  tars  for  use  as  dust  palliatives  and  road  binders,  or  for  the 
preparation  of  such  substances. 

Malthas. — Malthas  are  very  viscous  semiasphaltic  or  asphaltic  native 
bitumens  holding  an  intermediate  position  between  the  petroleums 
of  an  asphaltic  nature  and  the  native  asphalts.  As  a  rule  they  possess 
excellent  binding  properties.  They  constitute  the  binding  material 
of  many  bituminous  rocks  or  rock  asphalts,  and  in  this  capacity  often 
.serve  as  valuable  road  binders.  Many  malthas  have  a  tendency  to 
harden  rapidly  when  exposed  to  atmosjiheric  conditions,  and  this  prop- 
erty, while  accountable  for  an  increase  in  binding  value,  makes  them 
unsuitable  for  use  as  a  flux  in  the  preparation  of  asphaltic  cements. 

Malthenes. — A  term  commonly  applied  to  those  hydrocarbons  in 
petroleum,  petroleum  products,  malthas,  asphaltic  cements,  and  solid 
native  bitumens  soluble  in  both  carbon  bisulphide  and  paraffin  naph- 
tha, but  not  readily  volatile  at  temperatures  lower  than  108°  C.  (325° 
F.).  This  class  of  hydrocarbons  serves  as  a  valuable  permanent  flux- 
ing medium  for  the  so-called  asphaltenes  or  naphtha  insoluble  bitu- 
men in  asphaltic  cements,  giving  the  cement  any  desired  degree  of 
.softness  when  present  in  the  right  amount.  It  is  evident,  therefore, 
that  the  consistency  of  asphaltic  bitumens,  and  particularly  stable 

[Cir.  931 


BITUMENS    FOR   EOAD   CONSTRUCTION.  13 

asphaltic  cements,  is  largely  dependent  upon  the  relative  proportion 
of  naphtha  soluble  and  naphtha  insoluble  hydrocarbons.  The  same 
objection  to  the  use  of  the  term  "  asphaltenes  "  ^  applies  to  the  use  of 
the  term  "  malthenes.'' 

Mineral  Rubber. — A  term  sometimes  applied  to  artificial  bitumens 
of  rubbery  consistency,  usually  composed  of  a  mixture  of  gilsonite 
and  blown  petroleum  residuum. 

Naphthas. — Mixtures  of  hydrocarbons  of  low  boiling  points  occur- 
ring rarely  in  nature,  commonly  obtained  from  the  fractional  dis- 
tillation of  certain  bitumens.  Wlien  this  term  is  applied  to  low-boiling 
coal-tar  distillates,  it  is  usually  prefixed  by  the  words  "  coal  tar." 
The  word  "  naphtha  "  by  itself  is  generally  applied  to  low-boiling  petro- 
leum products.  Different  grades  of  naphtha  are  dijfferentiated  not 
only  by  their  boiling  points  but  also  by  their  specific  gravities,  which 
are  commonly  given  in  Baume  degrees.  Those  of  very  low  boiling 
points  and  specific  gravities  are  called  petrolic  ethers.  Naphthas 
vary  not  only  in  the  two  properties  above  mentioned  but  also  with  the 
type  of  petroleum  from  which  they  are  obtained.  Those  derived 
from  paraffin  petroleums  are  quite  different  chemically  from  naph- 
thas obtained  from  asphaltic  petroleums.  The  former  are  much  less 
powerful  solvents  for  asphaltic  substances  than  the  latter.  Paraffin 
naphtha  is  used  as  a  solvent  for  the  separation  of  certain  classes  of 
hydrocarbons  in  asphaltic  substances. 

Naphthalene. — A  solid  crystalline  highly  volatile  hydrocarbon  oc- 
curring principally  in  coal  tars  and  having  the  chemical  formula 
CioHg.  Its  presence  in  excessive  quantities  in  road  tars  is  believed 
to  be  detrimental,  as  it  possesses  no  binding  value  and  gradually  vola- 
tilizes from  the  tar,  leaving  it  hard  and  brittle. 

Native  Bitumens. — Mixtures  of  hydrocarbons  occurring  in  nature, 
which  may  be  gases,  liquids,  viscous  liquids,  or  solids,  but  if  solid  melt- 
ing- more  or  less  readily  upon  the  application  of  heat  and  dissolving 
in  carbon  bisulphide,  chloroform,  and  similar  solvents.  The  native 
bitumens  that  are  of  use  as  road  materials  are  petroleums,  malthas, 
asphalts,  and  other  solid  products  such  as  gilsonite  and  grahamite. 
Native  bitumens  often  contain  impurities  such  as  water,  inorganic 
matter  in  the  form  of  clay,  silt,  sand,  etc.,  and  extraneous  organic 
or  vegetable  matter. 

Oil  Asphalts. — Artificial  oil  pitches  or  asphaltic  cements  produced  as 
a  residuum  in  the  distillation  of  semiasphaltic  and  asphaltic  petro- 
leum. Many  of  these  products  are  blown  and  are  therefore  known 
as  blown  oils. 

Oil  Pitches. — More  or  less  hard  oil  asphalts. 

Oil  Tars.^ — Mixtures  of  hydrocarbon  distillates,  mostly  unsaturated 
ring  compounds,  produced  in  the  cracking  of  oil  vapors  at  high  tem- 

1  See  Asphaltenes.  ^  gpg  Bitumens.  ^  gee  Water-gas  tar. 

[Cir.  93] 


14  BirrMKNs  FOR  uo.M>  coNsrurcrioN. 

poratmvs.  Oil  (Hi's  are  usually  l>v-|>n)«ln<'ts  of  (lip  lUiunifacluro  of 
oil  pis  or  carluirottvl  waltM*  pis. 

Paraffin  Naphthas.-  Naphthas  consist in<x  of  a  niixturo  of  lijjht  vola- 
tiK'  hyilnH-arlions  of  (he  parallin  siM'ios.  oi-dinarily  ohlainod  as  lijj:ht 
tlistillatos  of  paraflin  potrolouni. 

Paraffin  Petroleum. — PotroloMni  the  base  of  which  is  composed  prin- 
cipally o{  the  i)araf]in  or  open-chain  series  of  hydrocarbons;  it  is 
thus  differentiated  from  asphallic  petroleums  which  are  composed 
largely  of  cyclic  or  rin<;  hydrcK-arbons.  Paraflin  petroleums  and  the 
uiuiltereil  residiies  pnxluced  by  their  distillation  are  of  inferior  value 
as  dust  palliatives  and  road  binders. 

Paraffin  Scale. — Solid  jiaraflins  recovered  by  distillation  and  pre- 
i  ipitaiionof  thedistillatesof  petroleumand  similar  materials.  The  per- 
centajre  of  paraffine  in  bitumen  is  usually  determined  in  this  manner. 

Paraffine. — The  term  paraffine  covers  a  number  of  gi'easy  ciystalline 
hydrocarbons  of  the  paraffin  series  occurring  as  dissolved  wax  in  cer- 
tain cla.sses  of  petroleum.  ^Mien  these  products  are  recovered  from 
petroleum,  they  constitute  the  commercial  product  paraffine.  Par- 
affine is  believed  to  be  detrimental  to  road  binders  in  which  it  occurs, 
and  it  is  certain  that  its  presence  in  excessive  amounts  indicates  infe- 
riority in  the  binding  value  of  the  material.  It  is  probable,  however, 
that  heavy  liquid  hydrocarbons  of  the  same  chemical  series  as  solid 
paraffine  exert  a  much  more  injurious  effect. 

Petrolenes. — An  ambiguous  term  sometimes  applied  to  those  hydro- 
carbons described  under  malthenes,  which  are  soluble  in  carbon  bi- 
sulphide but  insoluble  in  paraffin  naphtha,  and  sometimes  to  hydro- 
carbons in  petroleum  and  petroleum  products  volatile  at  or  below 
103°  C.  (325''  F.).  Owing  to  misconceptions  which  may  occur,  it 
would  seem  advisable  to  eliminate  the  use  of  this  term. 

Petroleums. — Petroleums,  or  mineral  oils,  are  fluid  native  bitumens 
of  variable  composition,  depending  largely  upon  the  locality  in 
which  they  occur.  There  are  three  general  types  of  petroleum  found 
in  the  United  States:  (1)  Paraffin  petroleums,  (2)  semiasphaltic 
petroleums,  and  (3)  asphaltic  petroleums.  Paraffin  petroleums  occur 
mainly  in  the  eastern  part  of  the  United  States  and  are  typified  by 
the  Pennsylvania  oils.  The  semiasphaltic  variety  occurs  in  the  south- 
ern and  middle  western  parts  of  the  United  States.  Texas  is  one 
of  the  main  sources  of  this  type.  Asphaltic  petroleums  occur  in  the 
western  part  of  the  United  States,  particularly  in  California. 
Petroleums,  if  of  semiasphaltic  or  asphaltic  character,  may  make 
excellent  dust  palliatives  and  road  binders  when  properly  treated. 

Petrolic  Ethers. — Very  light  volatile  naphthas  obtained  from  petro- 
leuni. 

Pitches. — Semisolid  or  solid  residues  produced  in  the  evaporation 
or  distillation  of  bitumens.     This  word  is  often  prefixed  by  the  name 

[Clr.  93] 


BITUMENS   FOR   ROAD   CONSTRUCTION.  15 

of  the  material  from  which  it  is  derived,  such  as  oil  pitch,  coal-tar 
pitch,  etc.  As  a  rule  the  term  pitch  is  confined  to  the  harder  re- 
siduums,  most  of  which  are  too  hard  for  use  as  road  binders  unless 
fluxed  with  a  more  fluid  product. 

Pyrobitumens. — Mineral  organic  substances  which  are  but  slightly 
acted  upon  by  the  solvents  for  the  bitumens,  but  which,  upon  being 
subjected  to  destructive  distillation,  give  rise  to  the  formation  of 
bitumens.  Pyrobitumens  are  derived  in  nature  both  from  bitumens 
and  direct  metamorphosis  of  vegetable  matter.  Among  the  former 
class  may  be  mentioned  Albertite  and  Wurtzilite,  and  among  the 
latter,  peat,  lignite,  and  bituminous  coal. 

Pyrogenetic. — Originating  from  the  action  of  heat.  Coal  tar  is  thus 
a  pyrogenetic  bitumen. 

Reduced  Petroleums  or  Reduced  Oils. — Residual  oils  produced  from 
crude  petroleum  by  the  removal  of  water  and  the  more  volatile  oil 
constituents,  without  chemically  altering  the  base  by  cracking  or  other 
means.  These  residues  are  often  made  by  distilling  the  crude  oil 
under  reduced  pressure.  Such  products  are  of  little  value  for  road 
treatment  unless  formed  from  semiasphaltic  or  asphaltic  oils. 

Refined  Tar. — A  more  or  less  viscous  tar  which  is  produced  by 
evaporation  or  distillation  of  crude  tar  until  the  residue  is  of  the 
desired  consistency.  This  term  also  includes  blown  tars  and  cut- 
back products  produced  by  fluxing  tar  pitches  with  volatile  or  non- 
volatile distillates.  Refined  tars  are  of  value  both  as  dust  palliatives 
and  as  road  binders  in  the  treatment  of  macadam  roads.  Their 
binding  value  is  proportional  to  their  hardness  within  certain  limits. 

Residual  Petroleums  or  Residual  Oils. — Heavy  viscous  residues  pro- 
duced by  the  evaporation  or  distillation  of  crude  petroleum  until  at 
least  all  of  the  burning  oils  have  been  removed  and  often  some  of  the 
heavier  distillates  as  well.  Residual  oils  grade  into  the  artificial 
asphalts  and  oil  pitches  as  their  hardness  and  viscosity  increase.  The 
more  fluid  products,  if  obtained  from  semiasphaltic  or  asphaltic 
petroleums,  serve  as  excellent  dust  palliatives  and  semipermanent 
road  binders  for  the  surface  treatment  of  roads.  The  more  viscous 
products  are  often  suitable  for  the  surface  treatment  of  roads  if  ap- 
plied hot,  but  are  seldom  of  value  in  road  construction  unless  pro- 
duced from  semiasphaltic  or  asphaltic  oils. 

Residual  Tars. — Heavy  viscous  residues  produced  by  the  evaporation 
or  distillation  of  crude  tar  until  all  of  the  light  oils  have  been  re- 
moved. Residual  tars  grade  into  the  tar  pitches  as  their  hardness 
and  viscosity  increase.  If  they  do  not  contain  an  excess  of  free 
carbon,  they  are  as  a  rule  well  adapted  for  use  as  binders  in  the  con- 
struction of  macadam  roads. 

Rock  Asphalt  or  Bituminous  Rock. — A  term  applied  to  a  great  variety 
of  sandstones  and  limestones  more  or  less  impregnated  with  maltha. 

[Cir.  93] 


l(')  Uni'MKNS    Foil    HOAl)    I'DNSTIirt'TlON. 

I)t'pik^ils  of  !«)H'h  miiti'riiil  nvc  widolv  (li.-.tnl>iil»'il  ovov  tho  I'liited 
Siatt'.<  iuul  varv  from  nuk  whifh  is  frinltlf  ami  wholly  drpiMulont 
uj)oii  tilt'  bitumen  to  hold  the  iniiiiMid  l"i:iu:iu»'ii(s  tojiri'tluM'  to  solid 
riH'k  lmviii«:  nioivly  its  intt>rs(iiTs  lilK'd  with  hitiiiiuMi,  Tlu'  fonuer 
ty^K"  is  i>f  valiio  for  uso  as  a  surfan*  hiiulor  in  (he  eonst ruction  of 
roads  when  the  maltha  shows  jjood  bindin*;  value  and  amounts  to  not 
le-^  thun  (■'  |H  r  <«Mit  of  tlu'  wciijht  of  ro*'k  asphalt. 

Semiasphaltic  Petroleums.  Scmiasphallic  petroleums  or  semi- 
asphiiltie  oil>-  are  petroK'ums  containiuir  a  seuiiasphaltie  base,  i.  e., 
petroleums  whose  residues  j)rodueed  l)y  e\aporation  or  distillation, 
while  itunpost'd  mainly  of  asphalt ic  hydrcKarbons,  contain  also  a  cer- 
tain pen^entrt^e  of  paralVm  wax.  They  thus  show  a  mixed  base.  If 
tlu'ir  percenta<j:e  of  heavy  parallin  hydiocarbons  is  not  excessive,  they 
may  be  made  to  protluce  ^"o<k1  dust  preventives  and  road  binders. 

Short. — A  tvrm  applied  to  l)ituminous  materials  which  are  non- 
thu'tile. 

Tar  Pitches. — Semisolid  or  solid  residual  tars.  Owing  to  the  gen- 
eral brittlene.ss  of  tar  pit<jhes,  only  the  softer  varieties  are  of  value 
in  their  natural  condition  as  road  binders.  The  harder  pitches  may, 
however,  be  used  for  this  purpose  if  fluxed  to  suitable  consistency 
with  heavy  or  dead  oil  distillates  of  tar. 

Tars. — Tars  are  artificial  or  pyrogenetic  bitumens  produced  as  dis- 
tillates by  the  destructive  distillation  of  bitumens,  pyrobitumens,  and 
other  organic  material. 

Water-Gas  Tars. — ^lixtures  of  liydrocarbon  distillates,  mostly  unsat- 
urated ring  compounds,  iDroduced  by  cracking  oil  vapors  at  high 
temperatures  in  the  manufacture  of  carbureted  Avater  gas.  Crude 
water-gas  tar  is  a  thin,  oily  liquid  having  a  specific  gravity  lying  usu- 
ally between  1  and  1.10.  As  a  rule  it  contains  a  considerable  quantity 
of  water,  which  is.  however,  largel}'  removed  by  mechanical  devices 
before  the  tar  is  placed  upon  the  market.  This  water  is  not  am- 
moniacal,  as  in  the  case  of  crude  coal  tars.  The  composition  of  water- 
gas  Uir  varie^s  with  the  character  of  the  oil  which  is  carbureted  and 
with  varying  conditions  attending  the  carbureting  process.  It  always 
shows  a  low  percentage  of  free  carbon,  usuall}^  less  than  2  per  cent, 
and  contains  little  or  no  naphthalene  unless  previously  used  for  scrub- 
bing coal  gas.  Crude  water-gas  tar  has  practically  no  binding  value 
and  is  serviceal>le  only  as  a  dust  palliative  in  the  surface  treatment 
of  roads.  When  reduced  to  proper  consistency  by  distillation,  how- 
ever, it  shows  certain  desirable  properties  for  use  as  a  road  binder 
both  for  surface  treatment  and  macadam  construction.  AVater-gas 
tar  may  also  be  used  in  the  preparation  of  road  binders  from  high- 
carbon  coal  tars.  "When  this  is  done,  the  two  crude  tars  are  mixed  in 
such  proportion  that  when  distilled  to  the  desired  consistency  the  mix- 
ture will  contain  le.ss  than  the  maximum  limit  of  free  carbon  allowable. 

[Cir.  ft.l] 

o 


